Female antisocial behavior in adolescence and late childhood has been associated with low basal cortisol levels. Because low cortisol has also been correlated with T helper cell Type 1 (Th1) predominance and suppression of T helper cell Type 2 (Th2), we investigated whether adolescent antisocial girls demonstrated this immunologic profile. Using plasma levels of IgG3 and IgG4 as markers for Th1 and Th2 activity, we studied IgG 3:4 ratios in 16-year-old girls with conduct disorder (CD) (n=42) or no psychiatric disorder (normal controls (NC)) (n=35). The mean IgG 3:4 ratio was higher in the CD group; this relationship remained significant after controlling for the effects of other variables. These data indicate that immunologic abnormalities are present in adolescent antisocial girls. Future studies should measure cytokine levels and investigate the clinical implications of these findings.